Vehicle occupant weight estimation apparatus

ABSTRACT

This invention describes an occupant size and weight detection device consisting of a combination of force/load sensors ( 1 ), a head position sensor ( 2, 3 ), a multidirectional acceleration sensor ( 5 ), and a seat position sensor ( 4 ) used to determine the weight of an occupant based on weight distribution, body angle and foot position. The goal of the invention is to determine the weight of an occupant who is sitting in the front seat of a vehicle that is subjected to the dynamic forces resulting from the vehicle moving. This technology can be used in applications such as automotive occupant weight and position sensing for use with safety devices such as airbags.

BACKGROUND OF THE INVENTION

[0001] Vehicle occupant protection systems, which are activated inresponse to a vehicle crash, for the purpose of mitigating occupantinjury are well known in the art. A vehicle may contain automatic safetyrestraint actuators such as front and side air bags, seat beltpretensioners, and deployable knee bolsters. The occupant protectionsystem may further include a collision/crash sensor for sensing theoccurrence of a vehicle crash and for providing an electrical signalindicative of the crash severity.

[0002] Several known occupant protection systems include an occupantclassification or weight detection system. The occupantclassification/weight detection system could consist of occupant size orweight determination on force/load sensors, capacitive/electric fieldsensors, resistive load distribution sensors, ultrasonic sensors,infrared sensors, and/or image based sensors. A controller, which isconnected to one or a combination of these sensors, controls theinflatable protection module in response to the sensed size or weight ofthe occupant. In response to the sensed occupant size or weight, one ormore deployment aspects of the air bag may be adjusted. A protectionsystem with adjustable aspects of deployment is commonly referred to asan “adaptive” protection system. Specifically, if the occupant is sosmall or light that deploying the air bag will not enhance protection ofthe occupant, it may be desirable to suppress actuation of the occupantprotection module. In such a case, deployment may even be moredetrimental than no deployment at all.

[0003] In any case, the determination of an occupant's size or weight isan important part of adaptive occupant protection systems. There areseveral types of size classification or weight determination systems. Asystem that classifies the occupant based on the strength of an electricfield (or the capacitance of the human body) may be fooled if a portionof the signal used to excite the sensor is lost. A system thatclassifies the occupant based on the load distribution, size, shapeand/or orientation of the occupant's posterior may not be reliablebecause varying people of varying heights and weights may haveposteriors with similar size and shape characteristics. A system thatrelies solely on force/load sensors cannot account for false readingsdue to external forces such as accelerations or losses due to body angleor foot position. Different obstacles such as a map, a book, or anewspaper could occlude signals from ultrasonic and video based systems.A lighter or cigarette could blind an infrared-based system.

SUMMARY OF THE INVENTION

[0004] The present invention is based on the fact that, in an occupantclassification or weight detection system, false readings due toexternal forces and losses due to body angle and foot position can becompensated for, if these factors can be detected and measured reliablyand consistently. This invention provides a simple, reliable method ofdetermining these factors and using them in conjunction with force/loadsensors to accurately determine an occupant's size and weight.

[0005] The system includes a seat-mounted sensor consisting of fourforce/load transducers and a multi-axis acceleration transducer assistedby a roof mounted occupant head position sensor, which are used todetermine the size and weight of an occupant who is sitting in a seatthat is subjected to the dynamic forces of a moving vehicle.

[0006] The roof mounted head position sensor provides the system withthe location of the occupant's head relative to the seat pan. A linearseat position sensor is used to track the position of the seat. The headposition sensor and the seat position sensor are used to find the bodyangle of the occupant. This value is used to bias the weight values readby the weight sensors. The acceleration sensors are used to determine ifand how other forces, such as acceleration, are influencing the weightsensor readings. An intelligent controller monitors theses sensors anddetermines the true weight of the occupant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 shows the position of all of the transducers in a vehicle.

[0008]FIG. 2 shows the position of the weight sensors in the seat.

[0009]FIG. 3 shows the position of the capacitive electrodes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0010] As FIG. 1 shows, the force/load sensors (1) are mounted in thefour corners of the seat pan. The first electrode (2) of the headposition sensor is mounted in a vehicle seat. The second electrode is anelement of the array (3) mounted to the ceiling of the vehicle above theoccupant's seat. A seat position sensor (4) is mounted between the seatpan and the supports. A three-direction acceleration sensor (5) ismounted rigidly under the seat. A control unit (6) continuously monitorsall of the sensors. The control unit (6) utilizes an excitation methodand a synchronous detection method to measure capacity. It uses a micropower low frequency signal that is safe for humans. The resulting weightmeasurement read by the force/load sensors is biased to account for bodyangle, foot position and external forces acting on the occupant.

[0011] In the preferred system, the force/load transducers measure theweight distribution on the seat pan. A weight is measured on each cornerof the seat pan. FIG. 2 shows the force/load transducers (1) are mountedon each corner of the seat pan (2), to the seat slide rails (3). Thesein turn connect to the seat frame. The configuration of thesetransducers allows the load on each corner of the seat pan to bedetermined. These sensors give the load distribution of the occupant onthe seat, i.e. the forces acting on each corner of the seat pan). Thesensors are covered by the seat cushion (4).

[0012] The system provides an occupant head position sensor, whichutilizes the human body's conductivity, to determine head position bymeasuring the capacity between the occupant's head and the roof-mountedarray of sensors (electrodes). A ceiling-mounted occupant head positionsensor may be incorporated in any type of vehicle that has a seat and aroof. Referring to FIG. 3, the principal components of theceiling-mounted proximity sensor of the preferred system are: a set ofelectrodes mounted in the base portion of the seat; a ceiling-mountedarray of second electrodes; a control unit which is connected to boththe first and second set of electrodes to provide the necessarymeasurements and calculations. The seat-mounted electrode providescapacitive connection with the occupant many times greater than thecapacity between the occupant's head and the roof-mounted array ofelectrodes. This connection allows for the consideration that theoccupant is coupled to the seat electrode. The capacity between theoccupant's head and the roof-mounted array of electrodes is a functionof the distance between them. The control unit uses an excitation methodto measure the said capacity.

[0013] The multi-axis acceleration transducer is used to determine ifexternal forces, such as accelerations, are influencing the weightreadings. These forces are measured in three directions: front-to-rear,side-to-side and up down. The acceleration in the front-to-reardirection allows the system to recognize if the vehicle isaccelerating/braking or if the occupant is leaning forward or backwards.The acceleration in the side-to-side direction allows the system torecognize if the vehicle is turning on an off ramp (or swerving aroundan obstacle) or whether the occupant is leaning to the side. Theacceleration in the up-down direction allows the system to recognize ifthe vehicle is going over bumps.

[0014] The system can also incorporate a seat inclination transducer tocompensate for an occupant sitting in a seat that is tilted back. Inthis situation a great deal of the occupant's weight maybe supported bythe backrest.

[0015] An intelligent controller monitors the force/load transducers andthe acceleration transducers to determine the weight of the occupant,and compensating for false readings due to external forces and lossesdue to body angle and foot position. This invention provides a simple,reliable method of determining these factors and using them inconjunction with force/load sensors to accurately determine anoccupant's size and weight.

[0016] Although the invention has been described in details withparticular reference to these preference embodiments, other embodimentscan achieve the same results. Variations and modifications of thepresent invention will be obvious to those skilled in the art and it isintended to cover in the appended claims all such modifications andequivalents.

1. A sensor for detecting the weight of an occupant in a vehicle seatcomprising: At least one load sensor coupled to a seat; A positionsensor determining the position of the occupant in the seat; and Acontroller determining the weight of the occupant based upon signalsfrom the at least one load sensor and position sensor.
 2. The sensor ofclaim 1 wherein the at least one load sensor provides an indication ofthe load distribution on the vehicle seat.
 3. The sensor of claim 2wherein the at least one load sensor comprises four weight sensors. 4.The sensor of claim 1 further including at least one accelerationtransducer measuring acceleration, said controller determining theweight of the occupant based upon an acceleration signal from theacceleration transducer.
 5. The sensor of claim 4 wherein the at leastone acceleration transducer measures acceleration in three axes.
 6. Thesensor of claim one further including a vehicle seatback angle sensor,said controller determining the weight of the occupant based upon asignal from the vehicle seatback angle sensor.
 7. The sensor of claim 1wherein the position sensor includes a seat electrode providing aconnection between the control unit and the occupant's body to transmitan electrical field.
 8. The sensor of claim 7 wherein the positionsensor further includes roof-mounted electrodes connected to thecontroller.
 9. The sensor of claim 8 wherein the controller uses asignal from each roof-mounted electrode in the array to compute theproximity of the occupant.
 10. The sensor of claim 1 wherein thecontroller determines the body angle of the occupant and uses it to biasmeasurements from the at least one load sensor in order to determine theweight of the occupant.
 11. A method for determining the weight of anoccupant in the vehicle seat including the steps of: (a) measuring aload on the seating surface; (b) determining an angle of the occupant inthe seat; and (c) determining the weight of the occupant based upon theangle and the load.
 12. The method of claim 11 wherein said step (b)further includes the step of determining the position of the occupant inthe seat.
 13. The method of claim 11 wherein said step (a) furtherincludes the step of measuring load distribution on the vehicle seat.14. The method of claim 11 wherein said step (a) further includes thestep of measuring load at a plurality of locations on the seat.
 15. Themethod of claim 11 further including the steps of: (d) measuringacceleration; and (e) determining the weight of the occupant in step (c)based upon said step (d).
 16. The method of claim 15 wherein said step(d) further includes the step of measuring acceleration in a pluralityof axes.
 17. A method for determining the weight of an occupant in avehicle seat including the steps of: (a) measuring load upon a seatingsurface; (b) measuring acceleration; and (c) determining the weight ofthe occupant based upon acceleration and the measured load.
 18. Themethod of claim 17 wherein said step (b) further includes the step ofmeasuring acceleration in a plurality of axes.